1. Field of the Invention
The present invention relates to a coil device preferably used for a resonance transformer and the like.
2. Description of the Related Art
Coil devices are used in various electrical products for various uses. For instance, in a lighting circuit for a backlight of liquid crystal display, a leakage transformer, which is as a resonance transformer for driving a display device with higher voltages, is generally used.
For a leakage transformer, as shown in the following Reference 1 for instance, a horizontal-type coil device, to which a scroll axis of coil is arranged parallel to a mounting substrate surface of the coil device, is known. Such horizontal-type coil device has a problem that a leakage flux toward upward and downward directions with respect to the mounting substrate surface is large.
In order to make the leakage flux small, it is considered that top and bottom of the horizontal-type coil device is covered with aluminum board or aluminum foil. However, with this, heat dissipation may be deteriorated.
Further, for other leakage transformers, as shown in the following Reference 2 for instance, a vertical-type coil device, to which a scroll axis of coil is arranged perpendicular to a mounting substrate surface of the coil device, is known. With its configuration, it enables to make the leakage flux toward upward and downward directions with respect to the mounting substrate surface small.
However, for conventional coil devices, a primary coil and a secondary coil are composed of wires wound by normal regular winding. Particularly, for the secondary coil which produces a high voltage, there is a problem with voltage withstandability since the start of winding wire for a first layer and the end of winding wire for a second layer closely contact with each other, and the voltage differences between them get larger. Further, for the regular winding, it is a way to wind one wire in a spiral way for a first layer and then to wind back on the first layer from end to start of the first layer for a second layer. For the subsequent layers, the same process is applied.
Further, as the frequency of voltage applied to a coil device gets higher, there is a problem with the current flow since wires, which are adjacent to each other, exert effects on each other. Furthermore, for the coil devices used for a leakage transformer, it is important to stabilize leakage characteristics. However, for the conventional coil devices wherein wires are wound in regular winding, there is a problem with the stability of leakage characteristics.    [Reference 1] Japanese Published Unexamined Application No: 2006-108390    [Reference 2] Japanese Published Unexamined Application No: 2005-158927